Cost-effective development of new pharmaceutical agents depends closely on the ability to prescreen drug candidates in high throughput cellular based assays. The compounds are tested not only for their ability to induce the desired effect on the target tissue, but also for a low side-effect profile in unrelated metabolic systems.
Since the liver controls the clearance and metabolism of most small-molecule drugs, a cornerstone of the screening process is to evaluate the effect on liver cells. One objective is to determine whether the compounds or their metabolites have any potential for hepatotoxicity—measured by an effect of the compound on cell viability, morphology, phenotype, or release of metabolites and enzymes that correlate with a compromise in cell function. Another objective is to evaluate the profile of metabolites produced from the compound, since the metabolites may have collateral effects on other cell types.
For this reason, there is a high commercial demand for high quality hepatocytes by the pharmaceutical industry. Tumor cell lines and cells from non-human mammals are often unsuitable for this process, and so pharmaceutical companies are often forced to use clinical samples and primary cultures of human cells. Because of supply and consistency issues, there is a strong need to identify a source that could provide large quantities of human hepatocytes having standardized and reproducible criteria of quality.
Hepatocytes may also be used to make bioartificial organs for clinical use. Such organs are needed to support individuals with impaired liver function as a part of long-term therapy and/or to bridge the time between a fulminant hepatic failure and hepatic reconstitution or liver transplant.
Unfortunately, culture systems for expanding human hepatocytes have been difficult to develop. European Patent Application EP 953 633 A1 proposes a cell culturing method and medium for producing differentiated human liver cells, apparently from donated human liver tissue. In most people's hands, the replication capacity of human hepatocytes in culture has been disappointing. As a remedy, it has been proposed that hepatocytes be immortalized by transfecting with large T antigen of the SV40 virus (U.S. Pat. No. 5,869,243). Alternatively, it has been proposed that a line of hepatocytes be developed that has had its replicative capacity increased using telomerase reverse transcriptase (WO 02/48319).